A radiation noise suppression circuit for a differential transmission line includes a differential transmission line which has plus line signal wiring of a differential signal and minus line signal wiring of the differential signal, and connects a differential driver and a differential receiver; signal GND wiring. A first impedance element and a second impedance element have substantially the same impedance value, and are connected in series between the plus line signal wiring and the minus line signal wiring at a location nearer to the differential receiver than a coil unit. A third impedance element is connected to a junction point. The first impedance element and the second impedance element are connected.